Removable electronics such as memory devices are commonly used as part of an electronic device. For example, devices such as computers, cameras, and other devices often use removable memory cards. The memory cards may be in different formats.
USB memory cards are known which include nonvolatile solid-state memory therein. However, other forms of memories may include different form factors, connector styles etc, making those other memories in essence incompatible with USB devices.
For example, Sony markets a memory that they call the memory stick. Other companies use SD memory, Compact Flash memory or others. In many cases, a smart card is also a form of memory that stores a memory therein. Some removable devices, such as smart cards or USB devices, in fact use a processor as part of the device.
When the removable device is put into a slot in the device, it fills the slot. Moreover, when you have a device that requires one kind of memory, you must buy that kind of memory to use in the device. However, USB memory has become ubiquitous since virtually all computers come with a USB slot. The USB memory is often intended to be removable and transportable.